1. Field of the Invention
The invention relates generally to waveguide equipment, production methods thereof, and intermediates thereof.
2. Background Art
In a connected portion and an end portion of an optical fiber cable for optical communications, waveguide equipment is used to connect the end of one optical fiber cable to, for example, another optical fiber cable, a light projection device, a photo detector, etc. Such waveguide equipment has been made of a quartz material of low loss in an infrared wavelength region. Recently, waveguide equipment with a polymer waveguide has been made of polymer material with low cost. For example, the waveguide equipment comprises the polymer waveguide on a silicon substrate.
Inventors of the present invention produced the waveguide equipment shown in FIG. 1 and FIG. 2. FIG. 1 is a perspective view of the waveguide equipment 1, and FIG. 2 is an exploded perspective view thereof. The waveguide equipment 1 comprises a waveguide 10 on a supporting substrate 2. The supporting substrate 2 is made of silicon and has a recess. The recess has spacers 3 and 4 formed at ends of an upper face of the supporting substrate 2. A V-shaped groove 5 to position an optical fiber is formed on a top surface of the spacer 4. The waveguide 10 is disposed on a lower surface of a cover substrate 6 made of glass. The waveguide 10 comprises an upper cladding layer 7 which is disposed on the lower surface of the cover substrate 6 and is made of transparent resins such as a polymethylmethacrylate (PMMA), a core 8 which is disposed on the lower face of the upper cladding layer 7 and is made of transparent resin with the refractive index higher than that of the upper cladding layer 7, and a lower cladding layer 9 which is disposed on the upper cladding layer to surround the core 8 and is made of the same resin as the upper cladding layer 7. This waveguide 10 is disposed between the spacers 3 and 4. The end portion of the core 8 and the groove 5 is in a straight line as viewed perpendicular to the upper face of the supporting substrate 2.
As for the waveguide equipment 1, not only one piece is produced in a manufacturing process. As shown in FIG. 3, multiple pieces are produced at one time by separating. FIG. 3 is a plan view to show a gathering of several pieces of waveguide equipment before separating. FIG. 4 is a sectional view of FIG. 3 cut by X1-X1 line. A number “2A” in FIG. 4 shows a supporting mother substrate which changes to the supporting substrate 2 by separating finally. A number “6A” of FIG. 4 shows a cover mother substrate which changes to the cover substrate 6 by separating finally. For example, the cover mother substrate is made of a glass wafer. For making the gathering of several pieces of waveguide equipment shown in FIG. 3, the recess having the spacers 3 and 4, and the groove 5 for multiple pieces are formed by etching on the upper surface of the supporting mother substrate 2A. On the other hand, the upper cladding layer 7 and the core 8 for multiple pieces are disposed on the lower surface of the cover mother substrate 6A. Next, cladding resin to form the lower cladding layer 9 is poured on the upper surface of the supporting mother substrate 2A. The cover mother substrate 6A is upside down and placed on the supporting mother substrate 2A, and the cladding resin is spread out between the supporting mother substrate 2A and the cover mother substrate 6A. The resin for cladding is formed at a certain thickness by pushing the spacers 3 and 4 to the lower surface of the upper cladding layer 7. In this state, the lower cladding layer 9 is formed between the supporting mother substrate 2A and the upper cladding layer 7 cured by exposure of the resin for the cladding to UV radiation. A number “11” in FIG. 4 is a dam part to prevent the resin for the cladding from overflowing into the groove 5.
After this, each piece of waveguide equipment 1 is made by separating the gathering by dicing along the dotted line as shown in FIG. 3. The cover substrate 6 and the upper cladding layer 7 are diced at a place corresponding to an inside edge of the spacers 3 and 4, and unnecessary parts of the cover substrate 6, the upper cladding layer 7 and the lower cladding layer 9 (resin for the cladding) are removed. The waveguide equipment 1 shown in FIG. 1 and FIG. 2 is provided by dicing an edge of the supporting substrate 2 and exposing an edge of the groove 5 at the end surface of the supporting substrate 2. If the resin for the cladding has a mask at a place opposed to the spacers 3 and 4, and the UV radiation does not reach the resin for the cladding, the cover substrate 6 and the upper cladding layer 7 corresponding to the spacers 3 and 4 can be removed easily. In addition, it is also permissible to remove the dam part 11 by cutting with the dicing blade.
As a result of making the waveguide equipment 1 as described above, however, minute wrinkles and voids occur in the lower cladding layer 9. This is because the cure shrinkage rate of the resin for the cladding is large (the cure shrink rate is around 10%). FIG. 5 is a plan view to show a sample with the whole resin for the cladding cured to examine the occurrence of the wrinkles. FIG. 6 is a sectional view of FIG. 5 cut by X2-X2 line. In FIG. 5, the part with the wrinkle 12 is expressed with a bold continuous line. It is easy for the wrinkle 12 to occur around spacers 3 and 4. In addition, a void also occurs with the wrinkle 12. When such wrinkle 12 and void occur, an appearance failure occurs to the waveguide equipment 1. Even more particularly, the upper cladding layer 7 and the core 8 is deformed by the residual stress, and there are problems due to the leakage of the optical signal propagating in the core 8 and a decrease of the optical signal propagation efficiency.
In addition, as shown in FIG. 7, when exfoliation 13 occurs between the upper cladding layer 7 and the core 8 by the cure shrinkage of the lower cladding layer 9, the waveguide equipment 1 becomes bad. Even more particularly, it becomes clear that the wrinkle 12 and the exfoliation 13 occur easier when the difference of height between the top surface of spacers 3 and 4, and the inner bottom surface of the recess is larger.
A resin with small cure shrinkage rate should be used to prevent such a characteristic deterioration. However, resin with small cure shrinkage rate is so expensive that the cost of the waveguide equipment 1 becomes high and the width of the resinous section becomes small. Therefore, an approach to prevent the characteristic deterioration by cure shrinkage without depending on a resinous kind is expected.